Dampening method and means for planographic printing



March 5, 1935. G, s, RowELL DAMPENING METHODAND MEANS FOR PLANOGRAP'HICPRINTING Filed sept. 19, 1932 Patented Mar. 5, 1935 Y PAT-ENT OFFICEnAMPENmG METHOD AND MEANS Fon.

- l rLANoGnAPmc rmN'rnzG George S. Rowell, Cleveland, Ohio, assigner toMultigraph Company, Wilmington, Del., a corporation of Delaware'Application September 19, 1932, Serial No. 833,824

12 Claims.

'This invention relates to a method and means for dampening planographicprinting plates and it comprises a dampening roller provided with acovering layer of a thixotropic glycerin gel, sometimes, but not always,mutually coextensive with a foraminous body such as sponge rubber or anopen-textured fibrous body as felt, all as more fully hereinafterdescribed and claimed.

Lithography, or planographic printing, depends upon the immiscibility ofoil and water. stated the process consists of applying a greasy image tothe surface of a dry printing plate and thereafter, during printing,maintaining the nonprinting areas of the plate in a damp andconsequently ink-repellent condition.

The use of water as a dampening fluid has several serious objections,among which may be mentioned the fact that it is volatile, that itsviscosity is very low and that a high degree of skill is required tofeed to and to maintain on the printing surface such a nicely adjustedamount of water as will protect the non-printing areas fromcontamination by ink and prevent the dampening iiuid from encroaching onthe printing areas with consequent degradation of the tinctorial valueof the printed image. These dilculties'have been long recognized in theart and many attempts have been made to eliminate or mitigate them.'I'hus it has been proposed to substitute glycerin or other viscousnon-volatile polyhydric alcohols of the saturated series for the usualdampening water. However, the viscosity of glycerin, whichmakes it muchmore effective than water, presents at` the same time a seriousdiillculty in that it has been found extremely dilcult heretofore toapply to the nonprinting areas a film which was both sumciently thin anduniform to avoid the detrimental effect produced by the aforementionedencroachment by the dampening fluid on the printing image. If the amountof glycerin on the non-printing areas be such that the ink rollerpassing thereover is capable of imparting substantial motion to theglycerin, a minute wave of glycerin is moved forward by the ink roll andis forced over the printing image. Because of its viscosity the glycerinproduces markedly greater degradation of the printed image than thatproduced by water under similar circumstances. In order to takeadvantage of the desirable characteristics of glycerin, i. e., itsviscosity and hygroscopicity, and avoid the heretofore insurmountabledimculties of obtaining from a glycerin-charged dampening roll asufficiently tenuous illmiform layer of glycerin over the non-printingareas without degradation Simply f of the printing image, it has beenlsuggested to incorporate the glycerin -as minute, dispersed emulsoidparticles inthe printingr ink itself, it

vhaving been discovered that such emulsoid ink,

when the ratio of Ldispersed glycerin to pigmented 5 oily vehicle wasproperly adjusted, would deliver a just adequate amount of glycerin tothe nonprinting areas. So far as the maintenance of the non-printingareas in an ink-repellent condition by an extremely thin Vfilmiformlayer of glycerin replenished from the ink carried by the ink roller,the process left nothing to be desired. The advantages derived from theuse of glycerin and its just adequate supply to the plate were, however,more than offset by the facts that such emulsoid inksv are unstable andtend to break, with separation of the glycerin from the pigmentedvehicle, in the ink fountain; that such emulsoid inks by reason of thecontained hydroscopic glycerin remain tacky for weeks and 20 sometimesfor months and after printing; and further that containing, as theymust, a substantial proportion of the non-pigmented fluid, i. e.glycerin, their covering power is greatly reduced and in consequence toobtain good tinctorial values such emulsoid inks must be so heavilyloaded with pigment as to adversely affect their physicalcharacteristics, as is well recognized by those skilled in the art.

It is an object of this invention to provide means whereby an extremelythinflmiform layer of glycerin, neithermotile nor mobile, may bedeposited on the non-printing areas of planographic printing plateswithout the necessity for human intervention or control. It is a furtherobject of this invention to provide means whereby such a film ofglycerin may be so replenished between successive inkings as toeffectively protect the non-printing areas of the plate fromcontaminationby ink throughout long editions, without the necessity foradjustment of the glycerin supply. Other objects and advantagesof theinvention will become apparent from its more detailed description.

I have discovered that a thixotropic glycerin gel, i. e. a glycerin gelwhich, although exhibiting the characteristic properties of a. solid gelwhen at rest, is capable of being liquefied by mechanical means and whenso liquefied tends to resume its previous gel state, may be so liqueedby frictional contact with the surface of a planographic printing plateas to leave thereon an extremely thin but continuous and unbrokenillmiform layer of glycerin which remains remarkably adherent to theplate. I believe the tendency for glycerin, derived from a thixotropicgel state, at least to the extent of a marked increase in viscosity in ashort period of time, accounts for the observed fact that a film of suchglycerin is less mobile and more resistant to grease under pressure, asof ink rollers passing thereover, than is a lm of ordinary glycerin ofthe same thickness.

The thixotropic effect is most markedly exhibited in glycerin gels whensuch gels are very delicate and I find it desirable therefore to providea foundation and at least a partial structural support for such gels,for use as the dampening means of this invention, by forming such gelsin part at least -in the interstices of a foraminous or open-texturedbase therefor. Both sponge rubber and felt have been found to besatisfactory for this purpose.

An understanding of the mechanical features of a dampening roll suitablefor the purpose of my invention may be had from an inspection of thedrawing in which:

Fig. 1 is an isometric view of a roller carrying a covering of`thixotropic glycerinv gel;

Fig. 2 is an enlarged sectional view of a portion of the rollerillustrated in Fig. 1 covered with sponge rubber; and

Fig. 3 is a similar view of a portion of the roller illustrated in Fig.1 covered with felt.

A mandrel 1, Fig. l, is covered with a continuous layer of a thixotropicglycerin gel 2. In Figs. 2 and 3 the disposition of a foraminous base 3in shown in section surrounding the mandrel 1, and permeated and coveredby the gel comprising the layer 2.

While for relatively short runs or small editions I find it satisfactoryto cast a covering layer of thixotropic gel directly on the mandrel, Iprefer to cover the mandrel with a thin layer, such as one-eighth of aninch, of sponge rubber, as in Fig. 2, felt, as shown in Fig. 3, or otherresiliently deformable material not detrimentally affected by moistureand to saturate this material with such a fluid mixture of glycerin andgelatin as will upon setting yield a thixotropic gel. By rotating theroll in a horizontal position while the glycerin-gelatin mixture issetting I may readily obtain a thin layer of gel covering the foraminousbase. In use it will be found that after the outer layer 2, in eitherFig. 2 or Fig. 3, has been liquefied by frictional contact with anddelivered to the non-printing areas of a planographic printing plate,the dampening roll of this invention will continue to deliver glycerinby reason of the resilient deformability of the foraminous base and itscomprised gel. For use on coarse grained plates I prefer to make the gelcovering co-extensive with the foraminous base in order that the amountof glycerin delivered to the plate by the liquefaction of the gel may belimited by the resilient deformability of the base and thus offset theincreased frictional effect of the coarse grain Iof the plate surface.

As the water content of commercial glycerin varies somewhat and as thegel consistency of gelatin-glycerin gels may vary as the gelatin mayvary from batch to batch, the ratios given in the following illustrativeformula should be considered as approximate only, but anyone skilled inthe art will have no difficulty in determining for any given lot ofglycerin and/or gelatin the ratio which will yield a gel of the desireddegree of thixotropia Formula: to 100 grs. of gelatin add 250 cc. ,ofwater containing 20 grs. of chloral hydrate; soaking for at least threehours, or preferably over night, adding to the mixture 300 cc. of waterand heat to between 60 C. and 65 C. until solution takes place andmixing equal parts of the dissolved gelatin and high-grade glycerin.This will yield on cooling to room temperature a solid. althoughdelicate, gel capable of exhibiting the thixotropic effect toapproximately the desired extent. Slight variations in the ratio of theglycerin-gelatin components will produce corresponding differences inthe stiffness of the gel and its thixotropic response to lightfrictional forces. It is to be noted that the liquefaction of thegelatin should be so carried out, preferably on a water bath at atemperature well below 70 C. because of the danger of the transformationof the gelatin by excessive heat into the nongelling state. It isfurther desirable that the chloral hydrate or other suitable germicide,such as hexylresorcinol, be added to the `water used to soften thegelatin in the rst instance. It may be Vstated in passing,'although thisfact is well known, that a germicide is required to prevent bacterialliquefaction of the gelatin. However, in the selection of such reagent,one should be chosen which is compatible or inert with respect to theplate or colloid or other image thereon. The precautions of maintainingthe temperature below 70, as above mentioned, apply as well to theliquefaction of the glycerin-gelatin gel by heating, for the purpose ofimpregnating foraminous material and coating the outer or roll surfacetherewith...

As pointed out in my copending application No. 631,588 it is sometimesdesirable to add such saltsas ammonium nitrate and ammonium -phosphateto glycerin used as a dampening fluid on metal printing plates andparticularly on zinc printing plates. When it is desired to include suchsalts in the dampening means of this invention it is merely necessary todissolve the desired amount in the water to be added to the softenedgelatin and when so added and the mixture brought to 60 C., more water,if needed, may be added until complete solution of salts and gelatin hasbeen effected. Dampening reagents which are suitable for application tothis invention include viscous liquid polyhydric alcohols such asglycerin, glycol, diethylene glycol, or others, having the commoncharacteristics of high viscosity and miscibility with water.

While the foregoing description has referred to gelatin, it will beobvious to those skilled in the art that Aga Aga, or other like materialmay be used without departing from the spirit and scope of the inventionas set forth in the following claims.

I claim:

1. Method of dampening planographic image bearing printing plates andlike surfaces, comprising the step of applying a thixotropic gelthereto.

2. Method of dampening planographic image bearing printing plates andlike surfaces, comprising the step of applying a thixotropic gel theretocontaining a viscous, liquid, polyhydric alcohol.

3. Method of dampening planographic image bearing printing plates andlike surfaces, comprising the step of applying a thixotropic glyceringel thereto.

4. Method of dampening planographic image bearing printing plates andlike surfaces, comprising the step of applying a thixotropic diethyleneglycol gel thereto.

5. Method of dampening planographic image bearing printing plates andlike surfaces, comprising the step of applying a thixotropicglycerin-gelatin gel thereto.

6. Method ,of dampening planographic printing plates and like surfaces,comprising the step of impregnating an open foraminous material with athixotropic gel and passing the impregnated material over the surface.

7. Method of dampening planographic printing plates and like surfaces,comprising the step of impregnating an open foraminous material with athixotropic gel and rolling the impregnated material over `the surface.

8. Means for dampening planographic printing plates and like surfacescomprising an open foraminous material impregnated with a thixotropicgel.

9. Means for dampening planographic printing plates and like surfacescomprising a roller, having an open foraminous material impregnated witha thixotropic gel.

10. Means for dampening planographic printing plates and like surfacescomprising an open foraminous material impregnated with a thixotropicgel containing a viscous, liquid, polyhydric alcohol.

11. Means for dampening planographic printing plates and like surfacescomprising an open foraminous material impregnated with a thixotropicgel containing glycerin.

12. Means for dampening planographic printing plates and like surfacescomprising an open foraminous material impregnated with a thixotropicgel containing diethylene glycol.

v GEORGE S. ROWELL.

